Research on Pitting Corrosion of Microalloyed High-Strength Steel Bars

In this study, a series of soaking experiments were conducted in a simulated marine environment solution to explore the pitting corrosion behavior induced by four types of inclusions in microalloyed steel bars: Al₂O₃, MnS, Al₂O₃-(Ti, V, Nb)N, and Al₂O₃-MnS-(Ti, V, Nb)N. In the early stage of corrosion, due to the high-density lattice distortion zone around the MnS and Al₂O₃ inclusions, along with the fact that these inclusions are not closely connected with the steel matrix, microcracks can occur leading to the initial corrosion of MnS in the Cl⁻ environment. The corrosion rate of Al₂O₃ is the second highest after MnS, and clusters of Al₂O₃ can further accelerate the corrosion rate. The lattice distortion density around (Ti, V, Nb)N precipitates is significantly lower than that around MnS and Al₂O₃ inclusions. Additionally, (Ti, V, Nb)N is closely connected with the steel matrix without any microvoids. Therefore, (Ti, V, Nb)N is not sufficient to induce pitting corrosion of the matrix. The trend of pitting corrosion induced by the four types of inclusions, Al₂O₃, MnS, Al₂O₃-(Ti, V, Nb)N, and Al₂O₃-MnS-(Ti, V, Nb)N, is as follows: MnS > Al₂O₃ > Al₂O₃-MnS-(Ti, V, Nb)N > Al₂O₃-(Ti, V, Nb)N.